Rhenium(III) and technetium(III) complexes with 2-mercapto-1,3-azole ligands and X-ray crystal structures Elena Marchesi a , Andrea Marchi a, * , Lorenza Marvelli a, * , Maurizio Peruzzini c , Michele Brugnati a , Valerio Bertolasi b a Laboratorio di Chimica Inorganica e Nucleare, Dipartimento di Chimica, Universita ` di Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy b Centro di Strutturistica Diffrattometrica, Dipartimento di Chimica, Universita ` di Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy c Istituto di Chimica dei Composti OrganoMetallici, ICCOM CNR, Via Madonna del Piano snc, Area di Ricerca del CNR, 50019, Sesto Fiorentino, Italy Received 29 July 2004; accepted 6 September 2004 Available online 22 October 2004 Abstract Reactions of labile [MCl 3 (PPh 3 ) 2 (NCMe)] (M = Tc, Re) precursors with 1H-benzoimidazole-2-thiol (H 2 L 1 ), 5-methyl-1H-benzo- imidazole-2-thiol (H 2 L 2 ) and 1H-imidazole-2-thiol (H 2 L 3 ), in the presence of PPh 3 and [AsPh 4 ]Cl gave a new series of trigonal bipy- ramidal M(III) complexes [AsPh 4 ]{[M(PPh 3 )Cl(H 2 L 1–3 ) 3 ]Cl 3 } (M = Re, 1–3; M = Tc, 4–6). The molecular structures of 1 and 3 were determined by X-ray diffraction. When the reactions were carried out with benzothiazole-2-thiol (HL 4 ) and benzoxazole-2-thiol (HL 5 ), neutral paramagnetic monosubstituted M(III) complexes [M(PPh 3 ) 2 Cl 2 (L 4,5 )] (M = Re, 8, 9; M = Tc, 10, 11) were obtained. In these compounds, the central metal ions adopt an octahedral coordination geometry as authenticated by single crystal X-ray dif- fraction analysis of 8 and 11. Rhenium and technetium complexes 1, 4 and rhenium chelate compounds 8, 9 have been also synthe- sized by reduction of [MO 4 ] À with PPh 3 and HCl in the presence of the appropriate ligand. All the complexes were characterized by elemental analyses, FTIR and NMR spectroscopy. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Rhenium; Technetium; Thiolate complexes; Structures 1. Introduction The coordination chemistry of rhenium and techne- tium is currently attracting much attention due to the radionuclide-based application in radiopharmaceuticals. 99m Tc is the radionuclide of choice for use in diagnostic imaging due to its ideal physical properties (t 1/2 = 6.02 h, c-energy = 140 keV). Recently, 186/188 Re have been introduced in nuclear medicine as suitable b-emitting radionuclides for the therapy of malignant and degener- ative diseases [1,2]. The ultimate goal of these investiga- tions is to elucidate the molecular structures of 99m Tc- and 186/188 Re-based agents produced in very low concentrations at nanomolar scale. This may be achieved through the comparison of their chemical and physical properties with those of the corresponding compounds prepared at macroscopic scale with the long-lived isotope 99 Tc and with cold rhenium. In addi- tion, rhenium and technetium belong to the same group of the periodic table and therefore they may show simi- lar chemical properties and rhenium may be often used as a non-radioactive alternative to technetium. Chelates which contain nitrogen and sulfur donor atoms such as pyridine-2-thiolate ligands show an interesting coordi- nation versatility and may give an important contribu- tion as models for the development of diagnostic ( 99m Tc) or therapeutic ( 186/188 Re) radiopharmaceuticals [3]. 0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2004.09.010 * Corresponding authors. Tel.: +39 0532 291128; fax: +39 0532 240709. E-mail address: mg1@unife.it (A. Marchi). www.elsevier.com/locate/ica Inorganica Chimica Acta 358 (2005) 352–362